Generally, a pump for circulation of an insulating liquid and a cooler are employed for lowering the heat generated from the coil of a vehicle transformer. A plurality of insulation members (spacer) are provided between the coils of the transformer. This spacer serves to ensure the flow channel of the insulating liquid flowing to cool the coil, and to retain the coil when mechanical force is generated by shorting.
The capability of cooling the coil is proportional to the coil wet area that is the area of the coil in contact with the insulating liquid, i.e. the surface area of the coil minus the area of the coil in contact with the spacer, and the flow rate of the insulating liquid flowing along the coil surface. Accordingly, the cooling efficiency is improved by ensuring a larger coil wet area.
However, even if a larger coil wet area is ensured by widening the spacer interval, the coil may be buckled to cause damage of the transformer unless the interval is sufficient to withstand the mechanical force, when generated, due to shorting.
The technique of cooling the coil of a transformer is disclosed in, for example, Japanese Patent Laying-Open No. 9-134823 (Patent Document 1) directed to a transformer for a vehicle. Specifically, in oil and air feed cooling system, a low-voltage winding is wound around the perimeter of the leg of an iron core, and a high-voltage winding is wound around the perimeter of the low-voltage winding, forming a cooling oil path between the windings. This structure is disposed in a tank such that the cooling oil path is parallel to the bottom of the tank. Duct pieces are provided between each winding of the low-voltage winding and high-voltage winding at different intervals to form the cooling oil path.
Japanese Patent Utility Model Laying-Open No. 6-17215 (Patent Document 2) discloses a transformer winding, including a stacked layer of a disk winding wound a plurality of stages between inner and outer insulation tubes, and having rectangular spacer pieces forming an oil path between the disk windings of each stage, arranged radially and in plurality. The width dimension of the spacer pieces at the upper end side is sequentially reduced to satisfy the relationship of A>B, where A is the width dimension of the spacer pieces at the center region in the axial direction of the transformer winding, and B is the width dimension of the spacer pieces at an end side located at least at the upper side in the axial direction of the winding.
Patent Document 1: Japanese Patent Laying-Open No. 9-134823
Patent Document 2: Japanese Utility Model Laying-Open No. 6-17215